0.4 g mixture of NaOH, Na2CO3 and some inert impurities was first titrated with \({N \over 10}\) HCl using phenolphthalein as an indicator, 17.5 mL of HCl was required at the end point. After this methyl orange was added and titrated. 1.5 mL of same HCl was required for the next end point. The weight percentage of Na2CO3 in the mixture is _________. (Rounded-off to the nearest integer)
